1. Field of the Invention
The present invention generally relates to mobile station equipment, base station equipment, and a control method, and more particularly, to mobile station equipment, base station equipment, and a control method which are used to set a stand-by state of the mobile station in mobile communication systems.
2. Description of the Prior Art
In a mobile communication system such as a digital automobile telephone system, a variety of types of mobile station equipment such as a portable type, an on-vehicle type, and a portable on-vehicle-mountable type are used. In general, according to the type of the mobile station equipment, antenna configurations and transmission powers of the equipment are different. The portable and on-vehicle-mountable types of mobile station equipment may be moved to narrow spaces and into buildings to where the on-vehicle type of mobile station equipment cannot be moved. In this case, for the portable and on-vehicle-mountable types of mobile station equipment, a radio transmission path between a mobile station and a base station has a large transmission loss. And, a large multipath fading is caused by surrounding buildings and mountains, etc. As a result, a good transmission performance may not be necessarily obtained.
FIG. 1 shows a block diagram of a configuration example of conventional base station equipment. In FIG. 1, a transmit antenna 51 and a receive antenna 52 are respectively connected to corresponding antenna terminals of amplifier equipment 53. Ports of the amplifier equipment 53 are connected with transmitter/receiver shelves 55-1 to 55-3 through divider/combiner parts 54-1 to 54-3. Control inputs and outputs of the transmitter/receiver shelves 55-1 to 55-3 are connected to corresponding inputs and outputs of base-station control equipment 56. PCM-input-and-output terminals of the transmitter/receiver shelves 55-1 to 55-3 are connected to a PCM interface part 57. Further, the PCM interface part 57 is connected to synchronous terminal equipment 58 which is connected to a control center (not shown) through a transmission line.
The transmitter/receiver shelf 55-1 comprises transmitting-and-receiving parts 59-11 to 59-1N (N is a given number) which respectively correspond to a plurality of radio channels, and a shelf control part 60-1 generally controlling these transmitting-and-receiving parts 59-11 to 59-1N. The transmitter/receiver shelves 55-2, 55-3 also have the same configuration as that of the transmitter/receiver shelf 55-1.
FIG. 2 shows a block diagram of a configuration example of conventional mobile station equipment. In FIG. 2, an antenna 71-1 is connected to an antenna terminal of a transmit/receive duplexer 72, and a received signal from the antenna 71-1 is supplied to one input of a demodulator 74 through a receiving part 73-1. A received signal from an antenna 71-2 is supplied to the other input of the demodulator 74 through a receiving part 73-2. An output of the demodulator 74 is supplied to a TDMA part 75. The received signal passed through the TDMA part 75 is supplied to a codec (coder and decoder) 76 to be decoded. A decoded signal from the codec 76 is supplied to a speaker 77.
On the other hand, an output signal from a microphone 78 which forms a handset with the speaker 77 is supplied to the codec 76 to be coded. Coded signal from the codec 76 is supplied to a waveform-shaping part 79 through the TDMA part 75. A waveform-shaped signal from the waveform-shaping part 79 is supplied to a quadrature modulator 80, and modulates a carrier from a frequency synthesizer 82. The modulated carrier is supplied to a power amplifier 81, and is transmitted through the transmit/receive duplexer 72 and the antenna 71-1. Amplitude information of the waveform-shaped signal of the waveform-shaping part 79 is provided to the power amplifier 81 to control its operational point and increase its power efficiency. A receive local signal from the frequency synthesizer 82 is supplied to the receiving parts 73-1, 73-2. The TDMA part 75, the frequency synthesizer and the receiving parts 73-1, 73-2 are controlled by a control part 83, and specified signals of the control part 83 are supplied to a display/operation part 84.
In the above-mentioned base station equipment, a part of the transmitting-and-receiving parts installed in the transmitter/receiver shelves 55-1 to 55-3 is previously selected to be used for a control channel. Based on control from the base-station control equipment 56 and the shelf control part 60-1, through the control channel, broadcast information is transmitted repeatedly, and a radio channel is set. The previously selected transmitting-and-receiving part communicates and interfaces with networks through the PCM interface part 57 and the synchronous terminal equipment 59.
Next, an operation of the conventional mobile station equipment will be discussed. FIG. 3 and FIG. 4 show flowcharts of the operation of the conventional mobile station equipment shown in FIG. 2. In the control part 83 shown in FIG. 2, a single or a plurality of perch frequencies are previously set. In FIG. 3, when a power is turned on, one of the perch frequencies is set in the frequency synthesizer 82 by the control part 83 (step S1). The frequency synthesizer 82 generates the perch frequency thus set, and provides the local signal of the perch frequency to the receiving parts 73-1, 73-2 and quadrature modulator 80. The receiving part 73-1 measures receive signal strength L1 of a broadcast signal which is received from the base station on the radio channel of the perch frequency (step S2). The control part 83 compares the receive signal strength L1 with the minimum signal strength Lth1 (which is referred to as a threshold level, hereinafter) (step S3). The threshold level Lth1 is a reference level for a connection in a service zone defined by this base station. When the receive signal strength L1 is equal to or larger than the threshold level Lth1, the measured receive signal strength L1 and the perch frequency are stored in a memory (not shown) (step S4). And, when the receive signal strength L1 is smaller than the threshold level Lth1, such a storage process is omitted and the operation proceeds to the next step. The above-mentioned successive processes are repeated for all perch frequencies (step S5).
After the above processes in step S5 are completed, the control part 83 determines whether or not any perch frequency is stored in the memory (step S6). When the perch frequency is not stored in the memory, it is supposed that the mobile station is not in any radio zone (step S7). This condition is referred to as out-of-zone, hereinafter. In this case, the above-mentioned successive processes (step 1 to step 6) are repeated.
When any perch frequency is stored in the memory, the control part 83 sorts the perch frequencies stored in the memory in an order of higher receive signal strengths L1 (step S8). And, the control part 83 selects the perch frequency having the highest receive signal strength in a top priority from the sorted perch frequencies and sets the frequency synthesizer 82 to the a selected perch frequency (step S9). And, subsequently, with the receiving part 73-1, the control part 83 measures a receive signal strength L2 of the broadcast signal which is received on the selected perch frequency (step S10).
The receiving part 73-1 supplies the received broadcast signal to the demodulator 74. The demodulator 74 demodulates the broadcast signal, and generates a baseband signal. The TDMA part 75 analyzes the baseband signal based on a predetermined frame structure, and provides an analyzed result to the control part 83.
The control part 83 determines whether or not the broadcast signal is regularly received by examining data of the broadcast signal (step S1). When the control part 83 determines that the broadcast signal is not regularly received by the examination, the next higher-strength perch frequency in the order of the stored perch frequencies is set to the frequency synthesizer 82, and the successive processes of the steps S9 to S11 are repeated for that perch frequency (step S12). During these processes, when it is determined that the broadcast signal is regularly received by the examination of the data of the broadcast signal, the receive signal strength L2 of the broadcast signal is measured again through the receiving part 73-1 by the control part 83. And, the receive signal strength L2 is compared with the minimum signal strength Lth2 which permits a stand-by operation for receiving a call (step S11'). The minimum signal strength Lth2 is referred to as a down-link stand-by permission level.
When the control part 83 recognizes that the receive signal strength L2 is equal to or larger than the down-link stand-by permission level Lth2 in the above comparison, the process proceeds to the stand-by state mentioned later. When the control part 83 recognizes that the receive signal strength L2 is smaller than the down-link stand-by permission level Lth2, in the same way as the case that the broadcast signal is not regularly received, the frequency synthesizer 82 is set to the next higher-strength perch frequency in the sorted order of the perch frequencies. And, the processes of steps S9 to S11 are repeated in the sorted order until a condition L2.gtoreq.Lth2 is satisfied or a last frequency is set (step S12). The above-mentioned processes of the control part 83 from a power-on timing or the out-of-zone state to the stand-by state, steps S1 to S12 are referred to as an entering zone process, hereinafter.
In the stand-by state shown in FIG. 4, the control part 83 measures a receive signal strength L3 of the radio channel at a given time interval through the receiving part 73-1 (step S13). Then, the receive signal strength L3 is compared with the minimum signal strength Lth3 which permits the stand-by state to be continued (step S14). The least signal strength Lth3 is referred to a down-link stand-by degradation level, hereinafter. When the control part 83 recognizes that the receive signal strength L3 is equal to or larger than the signal strength Lth3 in the above comparison, the process is maintained at the stand-by state. When the control part 83 recognizes that the receive signal strength L3 is smaller than the signal strength Lth3, the mobile station is assumed to be out-of-zone, and the successive processes of steps S1 to S6 shown in FIG. 3 are carried out (step S7 shown in FIG. 3).
When the mobile station is in the stand-by state, the control part 83 supervises an operation from a user through the display/operation part 84. And, the control part 83 examines control information (for example, a selection calling command) which is received from the base station through the antenna 71, the transmit/receive duplexer 72, the receiving part 73-1, the demodulator and the TDMA part 75. Further, the control part 83 detects information (for example, a location registration request) for the mobile station transmitted from the base station based on the predetermined control procedures. Thereby, the mobile station may detect a call (step S15 in FIG. 4), and associated processes with the call are performed (step S16).
In the above processes, the control information (for example, a call request) generated in the control part 83 is put into the TDMA frame by the TDMA part 75. A bit sequence of the TDMA frame is filtered by the waveform-shaping process in the waveform-shaping part 79. And, a filtered signal from the waveform-shaping part 79 is converted to a .pi./4-shifted QPSK signal by the quadrature modulator 80, and is transmitted to the base station through the power amplifier 81 and the transmit/receive duplexer 71-1.
Next,an operation of the conventional base station equipment will be discussed. FIG. 5 shows a flowchart of the operation of the conventional base station equipment shown in FIG. 1. In the base station, the base-station control equipment 56 connected to the base station transmits and receives a variety of control information (for example, a selection calling command, a location registration request, a call request, etc.) with the mobile station equipment located in the radio zone defined by the base station through the base station equipment. And, when any control information from the mobile station equipment is received, the base-station control equipment 56 analyzes the control information (steps S17, 18 shown in FIG. 5), and processes adaptive to these analysis result of the predetermined plural processes are successively carried out (step S19).
In the above description, the down-link stand-by permission level Lth2 and the down-link stand-by degradation level Lth3 may be transmitted to the mobile station by the base station equipment along it with the broadcast information. However, to simplify the description, it is assumed that the mobile station equipment previously has the down-link stand-by permission level Lth2 and the down-link stand-by degradation level Lth3.
Next, a description will be given of disadvantages of the conventional mobile and base station equipment. FIG. 6 shows a conventional control sequence between the mobile station equipment and the base station equipment. In the conventional mobile station equipment, as shown in FIG. 6, when the broadcast information from the base station is regularly received on the control channel, and the receive signal strength of the control channel in the mobile station equipment (which is referred to as a down-link signal strength) is larger than the down-link stand-by permission level Lth2, the mobile station equipment is in the stand-by state on the control channel. The above process is carried out regardless of a level of a signal which the base station receives from the mobile station. Therefore, for the portable-type and the on-vehicle-mountable-type mobile station equipment in which the transmission power is relatively low, the receive signal strength detected in the base station (which is referred to as an up-link signal strength) may be extremely small as compared to the down-link signal strength in the mobile station.
Accordingly, a large difference between the transmission performance of the up-link and down-link radio lines between the base station and the mobile station occurs. In this case, the control signal may not be regularly transmitted and received between the base and mobile stations, and, thus, the radio transmission path for a call may not be established. Even if the radio transmission path is established, a sufficient speech quality of the call may not be obtained and a service quality may be degraded. Furthermore, by the degradation of the quality, a disconnecting process may be forcibly performed based on the control sequence.